The use of hydrogenated acrylonitrile-butadiene (HNBR) rubber in belts, particularly for automotive use, has been suggested in the past. See e.g. articles by Trevor A. Brown: "Compounding for Maximum Heat Resistance and Load Bearing Capacity in HNBR Belts", Rubber World magazine, October 1993, page 53, and "Using HNBR to Improve Belt Compounds", Rubber & Plastics News, Jun. 7, 1993, page 45. See also U.S. Pat. No. 5,405,690. There are, however, no suggestions on what the composition should be.
U.S. Pat. No. 5,405,690 discloses the use of HNBR modified with 20 to 60 ppw methacrylic acid and 10-60 ppw zinc oxide. The modified compound is noted as being commercially available as ZSC 2295 from the Nippon Zeon Company. It is also disclosed that the modified HNBR may be blended with a limited amount of HNBR. However, U.S. Pat. No. 5,405,690 is silent about the physical properties of the disclosed compound, and teaches that the compound must be bonded to another rubber layer of defined physical properties in order to obtain the desired adhesion characteristics.
The ZSC-2295 disclosed by U.S. Pat. No. 5,405,690 is a known commercially available composition. The 1997 Rubber World Blue Book disclosed that the composition is an HNBR modified with methacrylic acid and zinc oxide. Nippon Zeon also discloses this commercially available compound in DE 39 18 929 A1.
Fujiwara, in U.S. Pat. No. 5,599,246 and EP 674121A1, discloses using a modified HNBR, specifically using the ZSC-2295, in a belt composition. The modified HNBR is blended with unmodified HNBR, blending 10-40 ppw of the modified HNBR with 90-60 ppw of unmodified HNBR so that the amount of zinc methacrylate is between 4 to 20 percent of the rubber compound. Fujiwara teaches that if the amount of zinc methacrylate becomes greater than 20 ppw of the total rubber composition, fatigue of the tensile body occurs.
Saito, in U.S. Pat. No. 4,99,570, discloses a rubber composition comprising HNBR modified with 10 to 100 ppw of a zinc salt of a methacrylic acid. Silicic anyhdride is used for improving the abrasion resistance of the compound.
Klingender, in "Use of Highly Saturated Nitrile in Rubber Roll Coverings," discloses the uses and possible modifications to HNBR. Klingender discloses modifying HNBR with zinc oxide and methacrylic acid for improved tensile strength and elongation. Klingender discloses combining the modified HNBR with unmodified HNBR, resulting in high tensile strengths. However, the tensile strengths disclosed are unrealistic for use as taught since the formulations are pure gum recipes without any filler. t is taught that for reduced amounts of carbon black and high amounts of the modified HNBR, the tensile strength and elongation are increased. All of the compositions disclosed by Klingender are for the use of rubber rolls or roll coverings. While it is required that such rubber compositions exhibit a high tensile strength due to the repeated contact with opposing roller and the product being calendered, it is not required that the rubber composition exhibit a very high elongation since there will not be repeated flexing of the rollers.